The present invention is directed to DC motors, and more particularly to control of a polyphase, brushless DC motor used to move magnetic media, such as a disk of a hard-disk system, past a read/write element, such as a head, such as used in the technology known as Winchester Drives.
It is well known that conventional DC motors, including polyphase, brushless DC motors to which the present invention is directed, are highly efficient, and possess characteristics that make them suitable for a number of applications. In particular, brushless DC motors, which are particularly efficient, are favored as the moving force for such apparatus as rotating a mirror for laser printers, moving magnetic tape past a read/write head, or rotating the disk surface of hard-disk systems past a read/write head.
Polyphase, brushless DC motors require application of currents to armature windings in sequential order to produce torque-inducing flux for moving a rotor. DC currents are alternately switched about the armature windings to create various current paths that produce magnetic flux orientations in a synchronized fashion. The magnetic flux so produced results in a torque on the motor that causes rotational movement. In order to ensure that current is applied to the proper motor phase, (i.e., the most appropriate current path is selected through winding of the stator) in order to produce a torque at the most beneficial time, various sensing devices are used to provide positional information about the rotor.
One such device is a Hall effect device or "Hall Switch," although other devices such as optics, can be used. One problem with these sensing devices is that they are more prone to failures than the devices with which they are used, thereby significantly affecting the overall reliability of the apparatus that incorporates the sensing device. Additionally, incorporating these sensing devices in the motor structure itself increases the motors size, cost, complexity and power consumption--features not normally desirable.
It can be seen, therefore, that a significant improvement in motor design can be achieved if some other way were found to provide feedback information as to the rotational position of the rotor of a polyphase DC motor, without incorporating extra apparatus in the motor structure itself.